'\"
'\" Copyright 1989 Regents of the University of California
'\" Permission to use, copy, modify, and distribute this
'\" documentation for any purpose and without fee is hereby
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'\" The University of California makes no representations about
'\" the suitability of this material for any purpose.  It is
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'\" $Header: /cvsroot/PROCPLACE/pptinytcl/doc/CrtCommand.3,v 1.1.1.1 2001/04/20 15:03:06 karl Exp $ SPRITE (Berkeley)
'\" 
.so man.macros
.HS Tcl_CreateCommand tcl
.BS
.SH NAME
Tcl_CreateCommand, Tcl_DeleteCommand \- define application-specific command bindings
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
\fBTcl_CreateCommand\fR(\fIinterp, cmdName, proc, clientData, deleteProc\fR)
.sp
int
\fBTcl_DeleteCommand\fR(\fIinterp, cmdName\fR)
.SH ARGUMENTS
.AS Tcl_CmdDeleteProc (*deleteProc)()
.AP Tcl_Interp *interp in
Interpreter in which to create new command.
.AP char *cmdName in
Name of command to create or delete.
.AP Tcl_CmdProc *proc in
Implementation of new command:  \fIproc\fR will be called whenever
\fIcmdName\fR is invoked as a command.
.AP ClientData clientData in
Arbitrary one-word value to pass to \fIproc\fR and \fIdeleteProc\fR.
.AP Tcl_CmdDeleteProc *deleteProc in
Procedure to call before \fIcmdName\fR is deleted from the interpreter;
allows for command-specific cleanup.  If NULL, then no procedure is
called before the command is deleted.
.BE

.SH DESCRIPTION
.PP
\fBTcl_CreateCommand\fR defines a new command in \fIinterp\fR and associates
it with procedure \fIproc\fR such that whenever \fIcmdName\fR is
invoked as a Tcl command (via a call to \fBTcl_Eval\fR) the Tcl interpreter
will call \fIproc\fR
to process the command.  If there is already a command \fIcmdName\fR
associated with the interpreter, it is deleted.  \fIProc\fP should
have arguments and result that match the type \fBTcl_CmdProc\fR:
.nf
.RS
typedef int Tcl_CmdProc(
.RS
ClientData \fIclientData\fR,
Tcl_Interp *\fIinterp\fR,
int \fIargc\fR,
char *\fIargv\fR[]);
.RE
.RE
.fi
When \fIproc\fR is invoked the \fIclientData\fP and \fIinterp\fR
parameters will be copies of the \fIclientData\fP and \fIinterp\fR
arguments given to \fBTcl_CreateCommand\fR.
Typically, \fIclientData\fR points to an application-specific
data structure that describes what to do when the command procedure
is invoked.  \fIArgc\fR and \fIargv\fR describe the arguments to
the command, \fIargc\fR giving the number of arguments (including
the command name) and \fIargv\fR giving the values of the arguments
as strings.  The \fIargv\fR array will contain \fIargc\fR+1 values;
the first \fIargc\fR values point to the argument strings, and the
last value is NULL.
.PP
\fIProc\fR must return an integer code that is either \fBTCL_OK\fR, \fBTCL_ERROR\fR,
\fBTCL_RETURN\fR, \fBTCL_BREAK\fR, or \fBTCL_CONTINUE\fR.  See the Tcl overview man page
for details on what these codes mean.  Most normal commands will only
return \fBTCL_OK\fR or \fBTCL_ERROR\fR.  In addition, \fIproc\fR must set
\fIinterp->result\fR to point to a string value;
in the case of a \fBTCL_OK\fR return code this gives the result
of the command, and in the case of \fBTCL_ERROR\fR it gives an error message.
The \fBTcl_SetResult\fR procedure provides an easy interface for setting
the return value;  for complete details on how the \fIinterp->result\fR
field is managed, see the \fBTcl_Interp\fR man page.
Before invoking a command procedure,
\fBTcl_Eval\fR sets \fIinterp->result\fR to point to an empty string, so simple
commands can return an empty result by doing nothing at all.
.PP
The contents of the \fIargv\fR array are copies made by the Tcl interpreter
for the use of \fIproc\fR.  \fIProc\fR may alter any of the strings
in \fIargv\fR.  However, the \fIargv\fR array
is recycled as soon as \fIproc\fR returns, so \fIproc\fR must not set
\fIinterp->result\fR to point anywhere within the \fIargv\fR values
(call Tcl_SetResult
with status \fBTCL_VOLATILE\fR if you want to return something from the
\fIargv\fR array).
.PP
\fIDeleteProc\fR will be invoked when (if) \fIcmdName\fR is deleted.
This can occur through a call to \fBTcl_DeleteCommand\fR or \fBTcl_DeleteInterp\fR,
or by replacing \fIcmdName\fR in another call to Tcl_CreateCommand.
\fIDeleteProc\fR is invoked before the command is deleted, and gives the
application an opportunity to release any structures associated
with the command.  \fIDeleteProc\fR should have arguments and
result that match the type \fBTcl_CmdDeleteProc\fR:
.nf
.RS
.sp
typedef void Tcl_CmdDeleteProc(ClientData \fIclientData\fR);
.sp
.RE
.fi
The \fIclientData\fR argument will be the same as the \fIclientData\fR
argument passed to \fBTcl_CreateCommand\fR.
.PP
\fBTcl_DeleteCommand\fR deletes a command from a command interpreter.
Once the call completes, attempts to invoke \fIcmdName\fR in
\fIinterp\fR will result in errors.
If \fIcmdName\fR isn't bound as a command in \fIinterp\fR then
\fBTcl_DeleteCommand\fR does nothing and returns -1;  otherwise
it returns 0.
There are no restrictions on \fIcmdName\fR:  it may refer to
a built-in command, an application-specific command, or a Tcl procedure.

.SH KEYWORDS
bind, command, create, delete, interpreter
